In the manufacture of an optical disk, first a photoresist is coated, as a photosensitive material, on a glass substrate and a resultant substrate is used as an optical disk substrate.
Then the photoresist of the substrate is exposed with a beam, such as laser beam or EB, and information to be recorded is formed, as recesses, in the optical disk substrate and recorded as pit signals (pit string) in the optical disk substrate.
The resultant optical disk substrate is subjected to develop-processing. The information is copied from the optical disk master to provide a metal substrate stamper necessary to copy optical disks.
The copying is performed with the use of a metal substrate stamper to provide an optical disk as a finished product. In the manufacture of the optical disk, information recording is effected by exposing the photoresist on the optical disk substrate with the laser beam.
FIG. 24 is a schematic view showing a recording apparatus for such an optical disk substrate. An optical disk substrate 3 is placed on a stage 2 coupled to a spindle motor 1. The optical disk 3 is comprised of a glass substrate with a photoresist coated as a photosensitive material.
A one-axial slider 4 is arranged above the stage 2 and, at its moving end, an exposure beam optical head is provided as the exposure beam laser head 5. The optical head 5 allows a laser beam which is output from a beam exposure optical system 6 to be directed onto the optical disk substrate.
The one-axial slider 4 adopts a linear guide drive system, that is, allows the moving end with the optical head 5 mounted thereat to freely move in a radius direction of the optical disc substrate 3.
A computer 7 controls the rotation of a spindle motor 1 and the movement of the one-axial slider 4 and controls the outputting of a laser beam of a beam exposure optical system 6.
In the arrangement as set out above, the optical disk substrate 3 is rotated by the rotation of the spindle motor 1 and, in this state, the optical head 5 is slidably moved by the one-axis slider 4 in a one-axis direction, that is, in the radius direction of the optical disk substrate 3.
The recording of the exposure beam optical head 5 is carried out through its linear slide movement (a linear guide system) from a position of the outermost circumference radius R to that of the innermost circumference radius r on the optical disk substrate as shown in FIG. 25. At this time, the row of digital signals to be recorded is set orthogonal to the slide movement direction.
By doing so, a laser beam exiting from the optical head 5 is directed to a rotating resist-coated optical disk substrate 3. When, at this time, the directing of the laser beam is controlled in accordance with information, groups of information such as pits and grooves are recorded on the optical disk substrate 3.
At this time, the position of the optical head 5 is measured by a laser interferometer 4a and feedback-controlled at all times by a fine adjustment system, not shown. Thus, the resolution of the track pitch by such an exposure apparatus will be unconditionally determined by the resolution measured by the laser interferometer.
Further, at the linear scan drive system of the optical head 5, it is necessary to make the one-axis slider 4, etc., high in rigidity. For this reason, as the one-axis slider 4 use is made of, for example, a slider of a two-guide system.
Such a slider is of such a type as to be set astride the optical disk substrate and a resultant apparatus as a whole will become larger in weight and bulkier.
As a drive system of the exposure beam optical head 5, there are two types, one using a direct scan linear guide system and the other using a swing arm system as seen in the magnetic recording system of an HDD (hard disk drive).
The drive by the swing arm system is done, by moving the optical head 5 as shown in FIG. 25, in circular arc motion from the position of the outermost circumference recording radius R to that of the inner-most circumference recording radius r.
In such a system, the rotation center of the swing arm is located outside the optical disk substrate 3, so that the drive path of the optical head 5 has a given curvature and is nearly approximate to that of the linear guide system.
The position of the beam exposure head of the swing arm system is grasped by an encoder provided at a rotation shaft for driving the rotation center of the drive path. In consequence, the resolution of the track pitch in the swing arm system has also its limit decided by the resolution of the encoder.
In a case where a larger amount of information than the present state is recorded on an optical disk, it is necessary to shorten the distance between adjacent pit strings (track pitch). Accordingly the distance between the adjacent pit strings becomes shorter than a length of a single pit.
In order to effect high density recording, it is required that high accurate positioning be made with respect to a radial direction at a time of forming pits one by one.
In the current exposure apparatus, a motion error when the exposure optical head is moved emerges directly as an uneven track pitch and it is necessary to reduce such motion error to a minimum possible extent.
In order to satisfy this requirement, one method is by raising the resolution of a position detector for use in the exposure apparatus. In recent not steady advance of the encoder and laser interferometer and their high-cost tendency, in terms of their position resolution, there is a strong demand for a high-resolution exposure apparatus not depending upon the resolution of such position detectors.
In the respective drive systems, the position of the exposure optical head 5 or a table (slider) with an optical head incorporated thereon is controlled with the use of a linear encoder or laser interference range finder. A target to be inherently position-controlled is a condensed laser beam spot by which a resist is actually sensitized/recorded. However, the position of such a condensed beam spot is not directly observed and measured.
In the driving method using the conventional linear guide system or swing-arm system, a feed error is generated depending upon the resolution of the position detector used and a consequent uneven track pitch is produced, thus making it difficult to record information at a high density.
It is accordingly an object of the present invention to provide a method for manufacturing an optical disk master which provides a simpler and low-cost structure for ensuring high density recording.
Another object of the present invention is to provide an optical disk which can be copied with the use of the optical disk master for high density recording.